Thermoplastic vulcanizates (TPVs) are produced via dynamic vulcanization of non-miscible blends of a rubber and a thermoplastic, that is, the selective cross-linking of the rubber, while melt mixing with the thermoplastic. As a result, products are obtained which consist of cross-linked rubber particles dispersed in a thermoplastic matrix, which provides both the elasticity and melt processability of TPVs. Compare to their non-crosslinked TPE counterparts, TPVs have superior properties in terms of heat resistance, compression set, chemical resistance and tensile strength. The majority of commercial TPVs are based on blends of EPDM with polypropylene (PP), which are typically crosslinked using a phenol derivative.
Thermoplastic vulcanizates may advantageously be produced by employing a peroxide cure system. “Peroxide-cured EPDM/PP TPV” generally exhibit lower color and lower residues than phenolic-cured TPV products, while maintaining good thermal stability and good compression set. U.S. Pat. No. 3,806,558 discloses that ethylene propylene-diene terpolymers (EPDM) can be partially cured by dynamic vulcanization, in the presence of polypropylene, to provide reprocessable materials with good physical properties. The diene component in polymer chains improves the crosslinking efficiency, but results in poor environmental degradation resistance. Alternatively, an ethylene-alpha olefin copolymer without a diene group can be used as rubber phase in peroxide cured TPV. Reference JP 3359505 discloses a thermoplastic polymer composition with improved environmental degradation by using an ethylene-octene copolymer produced by metallocene catalyst. However, metallocene-catalyzed ethylene-octene copolymer has a significant level of unsaturated groups that are not optimized for crosslinking applications.
It would be desirable for many of these applications to have new TPV formulations that have improved compression set and other mechanical properties.
International Publication No. WO 2011/002998 discloses ethylenic polymers comprising low levels of total unsaturation. Compositions using such ethylene polymers and fabricated articles made from the same are also disclosed.
International Publication No. WO 2011/002986 discloses ethylene polymers having low levels of long chain branching. Films and film layers, made from these polymers, and having good hot tack strength over a wide range of temperatures, are also disclosed.
International Publication No. WO 2007/136497 discloses a catalyst composition comprising one or more metal complexes of a multifunctional Lewis base ligand, comprising a bulky, planar, aromatic- or substituted aromatic-group; and polymerization processes employing the same, especially continuous, solution polymerization of one or more α-olefins at high catalyst efficiencies. See also WO 2007/136496 and WO 2007/136494.
U.S. Pat. No. 5,272,236 discloses substantially linear olefin polymers having a melt flow ratio (I10/I2)≧5.63, a molecular weight distribution defined by the equation: Mw/Mn≦(I10/I2)−4.63, and a critical shear stress at onset of gross melt fracture of greater than about 4×106 dyne/cm2, and their method of manufacture. The substantially linear olefin polymers preferably have at least about “0.01 long chain branches/1000 carbons” and a molecular weight distribution from about 1.5 to about 2.5. The polymers have improved processability, and are useful in producing fabricated articles, such as fibers, films, and molded parts. See also U.S. Pat. No. 5,278,272.
JP3359505B2 discloses a thermoplastic polymer composition for resistance to environmental deterioration. The thermoplastic polymer composition comprises (A) 100 parts weight of an olefinic polymer, comprising ethylene and at least one kind of C3-C10 α-olefin (density of 0.85-0.91 g/cm3 and Mw/Mn of <3.0), (B) 5-100 parts weight of a propylene polymer, (C) 5-250 parts weight of an oil, (D) 0.02-3 parts weight of a radical polymerization initiator, and (E) 0.1-5 parts weight of at least one crosslinking auxiliary, selected from divinyl benzene and triallyl isocyanurate. The composition can be obtained by heating and kneading the components, except the component C, to partially crosslink the mixture, and then subsequently adding the component C.
EP 0751182A1 discloses an olefin thermoplastic elastomer composition comprising 10 parts to less than 60 parts, by weight, of a crystalline polyolefin resin (A), and 90 parts to more than 40 parts, by weight, of an ethylene/α-olefin/nonconjugated polyene rubber (B). The rubber (B) is obtained by random copolymerization of ethylene, a C3-C20 α-olefin, and a nonconjugated polyene, in the presence of a metallocene catalyst.
U.S. Pat. No. 6,548,600 discloses rheology-modified thermoplastic elastomer compositions, comprising a melt blend of an ethylene/α-olefin polymer and a high melting polymer, such as polypropylene or a propylene/α-olefin copolymer. The rheology modification is induced by a combination of a peroxide and a free radical coagent. The resulting composition has an elastomeric phase, a non-elastomeric phase, and certain physical properties that exceed those of a like composition that is rheology-modified by peroxide alone. The compositions can be used to make a variety of articles of manufacture, such as automotive instrument panel skins, via calendaring and thermoforming procedures.
Additional polymer compositions are disclosed in the following references: U.S. Pat. Nos. 6,121,383, 6,147,160, 6,277,916, 6,476,132, 6,774,186, 4,130,535, 5,672,660, 4,948,840, 7,906,586, 7,338,994; US Publication Nos. 2002/0151647, 2007/0021564, 2007/0037931, 2006/0199910, 2002/0151647, 2007/0167575; and EP1940945B1.
There remains a need for TPV compositions with improved compression set and mechanical properties. There is also a need for such compositions that have reduced rubber particle size (and thus higher surface area and interface volume fraction) and increase the interfacial adhesion between the rubber phase and the plastic phase (all as indicated by improved mechanical properties). Compatibility and diffusion parameter of the rubber and thermoplastic affect interface thickness and interpolymer entanglements, and thus determine the size of the dispersed phase particle size and the mechanical and elastic properties. These needs and others have been met by the following invention.